This invention relates generally to inside diameter saws for slicing semiconductor wafers and more particularly to apparatus for dressing cutting surfaces of inside diameter saws.
One apparatus used for slicing ingots of monocrystalline semiconductor material into wafers is an inside diameter saw having a thin annular saw blade with cutting surfaces surrounding a central opening in the blade. The cutting surfaces have diamonds embedded in a layer of nickel for cutting the ingots. As the blade slices the ingots, semiconductor material dust and debris collect between the diamonds on the cutting surfaces thereby reducing the ability of the saw blade to cut through the ingot and increasing the cutting resistance of the blade. Moreover, the diamonds chip which also reduces the ability of the blade to cut through the ingot and increases the cutting resistance.
Cutting resistance during slicing causes the blade to deflect transverse to the cutting direction and out of the plane of the blade. If sufficiently large, this deflection can produce undesirable warpage, saw marks and thickness variations in the sliced wafers. The warpage cannot be eliminated by subsequent operations such as lapping. Even though saw marks and thickness variation can be eliminated by increasing stock removal in subsequent operations, the resulting material loss and time inefficiencies are highly undesirable.
The cutting resistance encountered by the blade is primarily a function of the amount of dust and debris lodged between the diamonds on the cutting surfaces of the blade. To limit the cutting resistance and resulting blade deflection, it is standard industry practice to dress the cutting surfaces of the blade using a special dressing stone to remove the dust and debris from between the diamonds on the cutting surfaces. In addition, dressing removes some of the nickel holding the diamonds in place so more of the diamonds are exposed. To dress the cutting surfaces, the dressing stone is pushed against the cutting surfaces of the blade. The dressing operation is critical to controlling the quality of the wafers sliced.
Various equipment and methods have been employed for dressing the cutting surfaces of inside diameter saws. Some saws include dedicated apparatus for dressing the cutting surfaces. Frequently, these dedicated apparatus are adapted to measure the warpage of the wafers cut or the deflection of the saw blade and to automatically dress the saws when needed. However, these apparatus are relatively complicated and expensive to operate since a separate apparatus (frequently including dedicated measurement equipment) is needed for each saw. Another type of saw dressing apparatus is portable so that it may be moved from saw to saw as needed. Generally, these portable apparatus are manually controlled by an operator who physically pushes the dressing stone against the saw blade. The portability of these apparatus results in reduced apparatus cost, but the manual operation increases the variability of the dressing process since it is highly dependent upon the subjective judgment and actions of the saw operator. Consequently, a dressing operation performed using such portable apparatus does not always result in the desired correction of cut.